A semiconductor integrated circuit includes a transistor layer formed on a semiconductor substrate, and a wiring layer formed on the semiconductor substrate to connect transistors. Transistors and wiring patterns are determined at a design stage of the integrated circuit, and thus a connection between the transistors cannot be changed after production of the semiconductor integrated circuit. On the other hand, in a reconfigurable programmable logic integrated circuit such as a field programmable gate array (FPGA), circuit information about an arithmetic operation, a wiring connection, and the like is stored in a memory, thereby enabling to change the wiring connection after production of the programmable logic integrated circuit.
Examples of memory elements for storing the circuit information include a static random access memory (SRAM) cell, an anti-fuse, a floating gate metal-oxide-semiconductor (MOS) transistor, and the like. However, these elements are formed in a layer in which transistors are formed, which results in an increase in chip area and an increase in production cost. In addition, an area of a wiring switch for changing a connection between logic operation circuits increases, which results in a reduction in a ratio of the logic operation circuits to the chip area. This leads to deterioration in operation speed of circuits mounted in an FPGA and an increase in operating power.
PTL 1 and PTL 2 disclose a programmable logic integrated circuit using a resistance-variable element as a memory element for storing circuit information. The programmable logic integrated circuit disclosed in PTL 1 and PTL 2 includes a resistance-variable element composed of a solid electrolyte material including metallic ions between a first wire and a second wire formed on an upper part of the first wire. A polarity of a voltage to be applied to the resistance-variable element is changed to thereby enable to change a resistance value of the element. A ratio of a low-resistance state (ON state) to a high-resistance state (OFF state) is the fifth power of 10, or more. Thus, the resistance-variable element functions as a switch for electrically connecting the first wire to the second wire, or disconnecting the first wire from the second wire.
The resistance-variable element can implement a memory function and a switch function, and thus a switch cell can be implemented by one resistance-variable element. According to PTL 1, a resistance-variable element is disposed at each intersection between a first wiring group and a second wiring group, and thereby a crossbar switch circuit capable of freely connecting any wire in the first wiring group to any wire in the second wiring group can be configured with small dimensions. As a result, a chip area can be reduced and operation performance can be improved by increasing a ratio of logic operation circuits on a chip. Further, since the resistance-variable element is non-volatile, there is another advantage that time and labor for loading circuit information at a time of start-up can be saved.